U.S. patent application number 11/488264 was filed with the patent office on 2007-01-18 for sensor for detecting arcing faults.
Invention is credited to Kim R. Fowler, H. Bruce III Land.
Application Number | 20070014060 11/488264 |
Document ID | / |
Family ID | 37661452 |
Filed Date | 2007-01-18 |
United States Patent
Application |
20070014060 |
Kind Code |
A1 |
Land; H. Bruce III ; et
al. |
January 18, 2007 |
Sensor for detecting arcing faults
Abstract
The present invention is directed to a sensor for detecting
arcing faults, the sensor combining a photodetector, a pressure
detector, and an accelerometer along with integrated circuitry. The
circuitry controls each detector, operates the self-test circuitry,
conditions the signals from the detectors, and communicates with
the external network. The circuitry receives commands from the
network and transmits the output decision from the sensor.
Inventors: |
Land; H. Bruce III; (Laurel,
MD) ; Fowler; Kim R.; (Windsor Mill, MD) |
Correspondence
Address: |
THE JOHNS HOPKINS UNIVERSITYAPPLIED PHYSICS LABORA;OFFICE OF PATENT
COUNSEL
11100 JOHNS HOPKINS ROAD
MAIL STOP 7-156
LAUREL
MD
20723-6099
US
|
Family ID: |
37661452 |
Appl. No.: |
11/488264 |
Filed: |
July 18, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60700069 |
Jul 18, 2005 |
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Current U.S.
Class: |
361/42 |
Current CPC
Class: |
H02H 1/0023
20130101 |
Class at
Publication: |
361/042 |
International
Class: |
H02H 3/00 20060101
H02H003/00 |
Claims
1: A photosensor comprising: a photodetector, an amplifier
connected to said photodetector, a filter connected to said
amplifier, a threshold comparator connected to said filter, a
storage element connected to said threshold comparator, an
amplifier having an amplifier input and two amplifier outputs, said
amplifier input connected to said storage element and said
amplifier output transmitting signals outside of said photosensor,
a differential receiver having two differential receiver inputs and
one differential receiver output, said two differential receiver
inputs connected to said two amplifier outputs, and said
differential receiver output connected to said storage element.
2: A photosensor comprising: a photodetector, an amplifier
connected to said photodetector, a filter connected to said
amplifier, a threshold comparator connected to said filter, a
microcontroller connected to said threshold comparator, a
differential transceiver connected to said microcontroller and
providing communication signals outside of said photosensor.
3. The photosensor of claim 2, wherein said microcontroller is a
DSP.
4. The photosensor of claim 2, wherein said microcontroller is a
FPGA.
5. The photosensor of claim 2, wherein said microcontroller is a
ASIC.
6: A pressure sensor comprising: a pressure-activated switch, a
filter circuit connected to said pressure-activated switch, a
storage element connected to said filter, an amplifier having an
amplifier input and two amplifier outputs, said amplifier input
connected to said storage element and said two amplifier outputs
transmitting signals outside of said pressure sensor, a
differential receiver having two differential receiver inputs and
one differential receiver output, said two differential receiver
inputs connected to said two differential receiver outputs from
said amplifier, and said differential receiver output connected to
said storage element.
7: A pressure sensor comprising: a pressure-activated switch, a
filter connected to said pressure-activated switch, a
microcontroller connected to said filter, a differential
transceiver connected to said microcontroller and providing
communication signals outside of said pressure sensor.
8. The photosensor of claim 7, wherein said microcontroller is a
DSP.
9. The photosensor of claim 7, wherein said microcontroller is a
FPGA.
10. The photosensor of claim 7, wherein said microcontroller is a
ASIC.
11: A pressure sensor comprising: a pressure-activated strain
gauge, a difference amplifier connected to said pressure-activated
strain gauge, a filter connected to said differential amplifier, an
analog-to-digital converter connected to said filter, a
microcontroller having an input and at least two outputs, connected
at said microcontroller input to said analog-to-digital converter,
connected at one output to said pressure-activated strain gauge,
and providing signals to the outside of said pressure sensor; a
pressure pump connected to said microcontroller.
12. The pressure sensor as in any one of claims 11 and 25, in which
said microcontroller is a DSP.
13. The pressure sensor as in any one of claims 11 and 25, in which
said microcontroller is a FPGA.
14. The pressure sensor as in any one of claims 11 and 25, in which
said microcontroller is a ASIC.
15: A pressure sensor comprising: a nozzle, a diaphragm connected
to said nozzle, said diaphragm comprising a strain gauge or a
built-in pressure switch, an ambient chamber connected to said
diaphragm, a bleed tube connected to said ambient chamber, a
substrate on which said nozzle, said diaphragm, said ambient
chamber and said bleed tube are mounted.
16. A sensor module for detecting arcing faults, said sensor module
comprising: a photodetector, a pressure detector, an accelerometer,
processing circuitry connected to each of said photodetector, said
pressure detector and said accelerometer, and wherein said
photodetector, said pressure detector, said accelerometer and said
processing circuitry are mounted to a single substrate.
17. The sensor module of claim 16, wherein said processing
circuitry comprises: photodetection circuitry comprising an
amplifier connected to a threshold comparator, accelerometer
processing circuitry comprising a difference amplifier connected to
a filter and an analog-to-digital converter connected to said
filter, and pressure detection processing circuitry comprising a
difference amplifier connected to a filter and a analog-to-digital
converter connected to said filter, wherein each of said
photodetection circuitry threshold comparator, said accelerometer
processing circuitry analog-to-digital converter, and said pressure
detection processing circuitry analog-to-digital converter are
connected to a microcontroller.
18. The sensor module of claim 17, wherein said microcontroller is
a DSP.
19. The sensor module of claim 17, wherein said microcontroller is
a FPGA.
20. The sensor module of claim 17, wherein said microcontroller is
a ASIC.
21. A sensor for detecting arcing faults, said sensor comprising: a
plurality of photodetectors, a plurality of pressure detectors, a
plurality of accelerometers, processing circuitry connected to each
of said photodetector, said pressure detector and said
accelerometer.
22. The sensor of claim 21, wherein said microcontroller is a
DSP.
23. The sensor of claim 21, wherein said microcontroller is a
FPGA.
24. The sensor of claim 21, wherein said microcontroller is a
ASIC.
25. A pressure sensor comprising: a pressure-activated strain
gauge, a difference amplifier connected to said pressure-activated
strain gauge, a filter connected to said differential amplifier, an
analog-to-digital converter connected to said filter, a
microcontroller having an input and at least two outputs, connected
at said microcontroller input to said analog-to-digital converter,
connected at one output to said pressure-activated strain gauge,
and providing signals to the outside of said pressure sensor, a fan
connected to said microcontroller.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is related to U.S. Provisional Application
No. 60/700,069, entitled "Integrated Sensor With Photodetector,
Pressure Detector, Accelerometer, and Circuitry for Detecting
Arcing Faults," filed on Jul. 18, 2005, which is incorporated
herein by reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an integrated
multifunctional sensor for detecting arcing faults. More
specifically, it relates an integrated multifunctional sensor for
detecting arcing faults, which combines multiple detection
phenomenologies to achieve high probability of detection and low
false alarm rate.
[0004] 2. Description of the Related Art
[0005] Arcing faults are essentially high-impedance short circuits
in power supply systems. In more precise language, an arcing fault
may be defined as a variable impedance sustained luminous discharge
of electrical power across a gap in a circuit. These discharges
conduct sufficient current to sustain an arc but remain below the
trip threshold of circuit breakers. They typically start as inline
high-resistance caused by a dirty or loose connection; this
situation may be sustained for days or weeks. The heat from the
faulty connection eventually melts the connection causing an
in-line arc. The in-line arc then jumps phase to generate white-hot
heat that melts and consumes the metal in switchgear in a few
seconds.
[0006] An arc generates a searingly bright, white-hot light and a
pressure shockwave. An arc also generates high-frequency harmonics
on the power lines. Detectable arcs dissipate a significant amount
of power. The current of an arc depends on the voltage available
and the spacing of the conductors. While arcs can occur at
household voltages and currents, these arcs do most of their damage
due to the ignition of adjacent combustible material and are not
the focus of this disclosure. Arcs in main power distribution
centers occur at voltages of 400 V and above and disable the
distribution centers due to bulk vaporization of metals. The power
distribution center arcs are the main focus of this disclosure.
[0007] The rise time of an arc is in the nanosecond range. It
generates light and high-frequency harmonics immediately. A
shockwave travels at the speed of sound or about 340 m/s, and takes
about 2.94 milliseconds to travel one meter from the arc. An arc
sustained for a few hundred milliseconds begins to combust and to
destroy copper and steel in power distribution switchboards.
Testing has shown that if the arc is quenched within 250
milliseconds then the damage will not generally require the
replacement of components of the switchboard. If the arc time
extends to one second then collateral damage can include holes in
the sheet metal wall of the switchboard. This defines a range of
time between about 1 and 200 milliseconds within which a protective
system must detect, discriminate and extinguish an arc before
significant damage occurs.
[0008] Dirty and loose connections often are the genesis for arcing
faults. The conditions for an arcing fault often take some time to
develop. As dirt accumulates and connections loosen the circuit
increases in resistivity; this, in turn, generates heat. The heat
will bake off particulates of insulation from the conductors.
[0009] There are presently a variety of techniques and systems for
detecting arcing faults. Below are listed the main techniques along
with their deficiencies.
[0010] Arc-proof switchboards contain the damage but do not prevent
it. They are constructed from heavier steel to reduce the
likelihood of flying debris and they contain pressure relief panels
in the top of the switchboards to vent the hot arc gases away from
direct impingement upon personnel. Their high purchase price, high
installation costs and the down time needed to install them, make
arc-proof switchboards too expensive for use in existing
installations.
[0011] Multi-function monitoring (MFM) works by attaching current
transformers on every major cable entering or leaving a switchboard
or a network of switchboards. A smart box sums all of the currents
entering or leaving a circuit node. Any missing current is evidence
of an arc and results in opening the protective breakers.
Alternatively MFM systems sometimes look at noise on the power line
or at the absolute value of the currents compared to some reference
value. While these systems can be effective with cable arcs, they
are much less effective on bus bars due to the wide variation in
impedance bus bar geometries. Additionally in dense switchboard
groups the wide range in size of loads makes it difficult to
discriminate the currents lost to loads vs. that lost to an
arc.
[0012] Current relay techniques have a long history in the
electrical industry. Current transformers are attached to major
conductors and then connected to the appropriate relays. If the
currents in the various conductors of the circuit are out of a
predefined balance the circuit is interrupted by the relays. This
scheme can be useful to insuring a balance in the current between
multiple loads but they have not proven to be effective against
arcing. Additionally, consider that the current transformers and
relays required for current relaying and for the MFM require that
bulky expensive components be added to already cramped
switchboards.
[0013] Arc fault circuit interrupters (AFCI) are useful only on low
voltage circuits with amperage les than 20A. AFCIs work by looking
at the frequency, duration, or pulsing of high frequency noise on a
circuit due to low power sputtering arcs. While AFCIs work in
household environments, they incur problems with discrimination
between the noise from bad arcs and that of normal arcs due to
switch openings, filaments blowing, hair dryers, etc. Manufacturers
of AFCI generally believe that due to the discrimination issues
AFCIs will never work at higher voltages or in an industrial
environment.
[0014] ABB arc guard system has optical fiber technology coupled
with or without current detection. Coupling the optical signal with
a current threshold can cause the system to miss smaller arcs. The
use of fiber optics restricts the angle of view of the sensors and
worsens the sensitivity for smaller arcs. This system has no
Built-In Test (BIT) capability; therefore one can not be sure that
the system is on line and functioning correctly. It is geared to
protecting individual switchboards and may not be set up to look at
large switchboard networks in zone-oriented schemes. The arc guard
system may also have no predictive capability.
[0015] Thermal imaging of electrical switchboards can identify
faulty connections and components and direct preventive
maintenance; unfortunately typically less than half of all
connections are in view of the thermal imaging operator. Thermal
imaging is only effective if performed while the switchboards are
energized and up to their normal operating temperature. Thus the
process requires working on energized switchboards which is
difficult to perform and presents a safety hazard. Due to costs,
thermal imaging is only done every one-two years; however it can
only look forward a few days.
[0016] The Continuous Thermal Monitoring System (CTM) can prevent
arcing faults due to overheated connections by the detection of
pyrolysis products from the overheated connections. A CTM
indications directs the operator to perform preventative
maintenance in a given switchboard before an arc occurs. This
system is not effective against arcs caused by contamination or
falling objects.
[0017] A related patent is U.S. Pat. No. 4,658,322 Arcing Fault
Detector, by Neftali Rivera. The arcing fault detection system
disclosed in this patent comprises a plurality of temperature
sensors and a differential pressure sensor, with their intelligence
being processed by a fault protector which controls the tripping of
the circuit breaker(s). This patent further discloses the optional
use of photodiode(s), which may be used with or in place of the
temperature sensors to detect light generated by an arc fault.
While the system disclosed in this patent is capable of detecting
arcing faults which are accompanied by pressure, temperature and/or
light, the system has a high false alarm rate and other
deficiencies.
[0018] In summary, while these sensors accomplish their intended
purposes, their numerous serious deficiencies have been noted
above, and there remains a strong need for an arcing fault
detection system which has both a high probability of detection and
a low false alarm rate for a broad range of amperages and
fault-types, thus addressing and solving problems associated with
conventional systems.
SUMMARY OF THE INVENTION
[0019] The present invention is directed to a sensor for detecting
arcing faults, the sensor combining a photodetector, a pressure
detector, and an accelerometer along with integrated circuitry. The
circuitry controls each detector, operates the self-test circuitry,
conditions the signals from the detectors, and communicates with
the external network. The circuitry receives commands from the
network and transmits the output decision from the sensor. This
approach allows a combination of high probability of detection and
low false alarm rate which surpasses that attainable by
conventional systems.
[0020] It is an object of the invention disclosed herein to provide
a new and improved sensor for detecting arcing faults, which
provides novel utility and flexibility through the use of a unique
design which allows the sensor to achieve a high probability of
detection along with a low false alarm rate.
[0021] It is another object of the invention disclosed herein to
improve the early detection of arc faults in advance to help save
lives.
[0022] It is another objection of the invention disclosed herein to
improve the early detection of arc faults to save systems
explosions and costly repairs and replacement of equipment.
[0023] It is another object of the invention disclosed herein to
provide a new and improved sensor for detecting arcing faults,
which would approach arc detection from a system level that would
avoid the cascading of arcing failures through large groups of
switchboards; causing massive blackouts such as evidenced in the
Chicago Loop, New York City, and Wall Street.
[0024] It is another object of the invention disclosed herein to
present arc fault detection which contains built-in-test functions
that assure that the protection is fully functional and on line at
the time of need.
[0025] It is another object of the invention disclose herein to
present a multi-parametric sensor whose performance can be tailored
for optimal arc detection in a wide variety of environments.
[0026] It is an advantage of the invention disclosed herein to
provide a new and improved sensor for detecting arcing faults,
which is inexpensive and can be applied easily to existing
installations.
[0027] These and other objects and advantages of the present
invention will be fully apparent from the following description,
when taken in connection with the annexed drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] The teachings of the present invention can be readily
understood by considering the following detailed description in
conjunction with the accompanying drawings, in which:
[0029] FIG. 1 is a diagram showing an example of functional
components for a photosensor.
[0030] FIG. 2 is another diagram showing an example of functional
components for a photosensor.
[0031] FIG. 3 is a diagram showing an example of functional
components for a pressure sensor.
[0032] FIG. 4 is another diagram showing an example of functional
components for a pressure sensor.
[0033] FIG. 5 is a third diagram showing an example of functional
components for a pressure sensor.
[0034] FIG. 6 is a fourth diagram showing an example of functional
components for a pressure sensor.
[0035] FIG. 7 is a diagram of an example of an integrated sensor
module according to the principles of the present application.
[0036] FIG. 8 is a diagram of an electrical schematic of the
integrated sensor module of FIG. 7.
[0037] FIG. 9 is a diagram showing an example of multiple
integrated sensor modules according to the principles of the
present application.
[0038] FIG. 10 is a diagram showing an electrical schematic of the
multiple integrated sensor modules of FIG. 9.
[0039] FIG. 11 is a diagram showing an example of a pressure
shockwave encountering a detector array.
[0040] FIG. 12 is a diagram showing a schematic for power backup
for a generic sensor.
[0041] FIG. 13 is a flow chart of one possible algorithm for
running a generic sensor.
[0042] FIG. 14 is a flow chart of one possible algorithm for
detecting and qualifying an arcing fault.
[0043] FIG. 15 is a diagram of one possible combination of
accelerometer and pressure sensor.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0044] Referring now to the drawings in greater detail, FIG. 1 is a
diagram showing example functional components for a photosensor.
Photosensor 10 is shown with photodetector 11, amplifier 12, filter
13, threshold limiter 14, flipflop/storage/memory element 15,
communications transmitter 16 and differential driver/receiver
17.
[0045] FIG. 2 is a diagram showing another possible configuration
for a photosensor. Photosensor 20 is a more sophisticated
photosensor with built-in circuitry for generating complex
communication protocols and timing. Photosensor 20 is shown with
photodetector 21, amplifier 22, filter 23 and threshold limiter 24.
Threshold limiter 24 is shown connected to microcontroller 25. Note
that microcontroller 25 could also be a DSP or FPGA or ASIC for
controlling the photosensor and communicating with the central node
or network. Microcontroller 25 may include algorithms for timeout
durations. Microcontroller 25 is connected to differential
transceiver 26.
[0046] Photosensors 10 and 20 of FIGS. 1 and 2 respectively are
easily configured for BIT and BIST, although the circuit details
for including BIT and BIST have not been explicitly illustrated in
FIGS. 1 and 2. Further, these sensors can easily connect to any
type of network or central processing system or an embedded system
for protecting power switchboards against arcing faults. They fit
into either a centralized architecture such as the star-topology
connections or a distributed architecture such as a network.
[0047] FIGS. 3 and 4 are diagrams showing example functional
components for pressure sensors 30 and 40, respectively. In FIG. 3,
pressure sensor 30 is shown with pressure-activated switch 31
(though a strain gauge may be used as well), filter or debounce
circuit 32, a flipflop/storage/memory element 33, a transmitter 34
and differential driver/receiver 35. In FIG. 4, pressure sensor 40
is shown with pressure-activated switch 41 (though a strain gauge
may be used as well), filter or debounce circuit 42 and
microcontroller 43 (microcontroller 43 could also be a DSP or FPGA
or ASIC for controlling the photosensor and communicating with the
central node or network). Microcontroller 43 includes algorithms
for timeout durations. Microcontroller 43 is connected to
differential transceiver 44.
[0048] FIG. 5 is a diagram of example functional components for
pressure sensor 50 that uses a strain gauge element. Pressure pump
51 is used to supply a test pressure to the strain gauge element
upon command. A similar pressure pump or fan can be use with the
pressure switch 31 of FIG. 3 or 41 of FIG. 4. Its advantage is that
it tests the mechanism of the switch or strain gauge as well as the
associated electronics. The disadvantage is the added complexity.
Shorting across the switch or strain element is a simple way to
perform a test of the electrical components, but its disadvantage
is that it does not test the mechanism of the switch. This
application also supplies a filter/debounce circuit.
[0049] FIG. 6 illustrates example components in a more
sophisticated pressure sensor. More sophisticated pressure sensors
have built-in circuitry for generating complex communication
protocols and timing. FIG. 6 is a diagram showing micromechanical
(MEMS) embodiment 60 of a pressure sensor, with an entry nozzle and
a pressure detector configuration. An ordinary pressure sensor or
pressure switch may not properly respond to the high frequency
pressure generated by an arc. This pressure is a shockwave with
both a very sharp transient pressure wave and a high frequency
alternating pressure. Therefore, this application provides a
pneumatic rectifier 65 to pneumatically smooth the pressure seen by
the switch or strain gauge. Funnel-shaped entry nozzle 65 is
affixed to the input to the pressure sensor such that the large end
of nozzle 65 faces the potential arc and the pressure from the arc
is forced through the small end of nozzle 65 into a small cavity in
front of pressure sensing diaphragm 64. Diaphragm 64 includes a
strain gauge or built-in switch (not shown) to detect flexures from
pressure changes. This combination smoothes the rapidly-varying
pressure from the arc and allows the pressure detector to perform
correctly. Note that the principles of the present application may
be applied to a wide variety of designs for entry nozzle 65, hence
the specific configuration shown in FIG. 6 is not intended to limit
the scope of this application. Ambient chamber 62 is shown
relatively large compared to the front-side chamber and provides a
transient reference for differential pressure measurements. Ambient
pressure bleed tube 63 protrudes from ambient chamber 62 for
adjusting pressure levels. Substrate 61 is composed of bulk silicon
or other material. Substrate 61 provides a mounting surface and
also contains readout and signal conditioning and processing
circuitry.
[0050] Pressure sensors require acute sensitivity to detect an arc
before critical damage is done to the switchboard. Unfortunately,
changes in barometric pressure may cause the pressure detector to
erroneously report the presence of an arc. This problem can be
remedied by any one of the following three methods: First, a
differential pressure sensor can be used to compare the pressure
inside the switch board to that outside of the switch board. If the
inside pressure is higher than the outside pressure an arc is
likely present. The disadvantage of the method is that it requires
drilling a hole in the surface of the switch board.
[0051] The second method requires the use of a differential
pressure sensor. Here a small hole vents a cavity attached to the
back side of the pressure diaphragm. Barometric pressure changes
occur slowly and both sides of the diaphragm will thus see the same
pressure. No false signal will be created. If an arc occurs, the
air flow from the shockwave of an arc will enter the front side
more readily than the back side and thus correctly read the rise in
pressure caused by the arc. The small vent holes in the back side
cavity present a greater pneumatic resistance to air flow that
accompanies the shockwave of an arc, consequently pressure will
build up more slowly in the back side cavity than in front of the
diaphragm.
[0052] The third method uses an analog-to-digital converter (ADC)
and a microcontroller chip to measure the pressure continuously
inside the switch board. By monitoring the rate of change in
pressure, the microcontroller will easily discriminate between the
slow barometric pressure rise (or even a door slamming) an the
rapid rose in pressure due to an arc. The sensors of FIGS. 4, 5,
and 6 may equally be amenable to the use of all three of the above
techniques for discrimination.
[0053] The pressure sensors of FIGS. 3 through 6 are easily
configured for BIT and BIST, although the circuit details for
including BIT and BIST have been explicitly illustrated in FIG. 5.
Further, these sensors can easily connect to any type of network or
central processing system or an embedded system for protecting
power switchboards against arcing faults. They fit into either a
centralized architecture such as the star-topology connections or a
distributed architecture such as a network.
[0054] FIG. 7 illustrates an example of an integrated sensor
module. FIG. 7 shows one possible mechanical orientation and
location of the detectors. Integrated sensor module 70 may be a
single MEMS device or may be built-up from individual detectors and
circuits. The integrated sensor module 70 incorporates photodiode
detector 73 for detecting the bright flash from an arcing fault.
Also incorporated into integrated sensor module 70 is a pressure
sensor composed of entry nozzle 78, diaphragm 77, ambient chamber
75 and pressure bleed tube 76. Note that entry nozzle 78 may be
part of substrate 71 or built into the packaging around substrate
71. Also incorporated into integrated sensor module 70 is
accelerometer 74. Accelerometer 74 detects accelerations not
associated with pressure changes, and may be micromachined from
bulk silicon or other substrate material with sufficient air vents
to keep pressure on both sides of the bulk mass during pressure
changes. Accelerometer 74 is shown oriented in the same plane as
the diaphragm 77. Substrate 71 contains and supports the detectors,
and processing core 72. Processing core 72, whether it is a
microcontroller, digital signal processor (DSP), programmable
logic, or fixed binary logic, may read all the detectors, condition
(e.g., perform filtering, timing, threshold comparisons) and fuse
the data, and make a decision as to the validity of the detection.
For running self tests, both BIT and BIST, the sensor either has
algorithms in a multitasking environment or has a separate
microcontroller.
[0055] FIG. 8 is a diagram showing electrical schematic 80 of the
electrical circuit for integrated sensor module 70 shown in FIG. 7.
Light from the arc impinges on photodetector 73, which is connected
to amplifier 81, which connects into threshold comparator 82 and
then on to processing core 72. The sensor window 92 protects the
photodetector 73 and allows the reflection of light from an impeded
Light Emitting Diode (LED) 93 into the photodetector 73 for
Built-in-self-test (BIST). In a similar fashion,
acceleration-activated strain gauge 83 connects to difference
amplifier 84 which is connected to filter 85, which in turn
connects to analog-to-digital converter (ADC) 86 which provides a
digital signal to processing core 72. Likewise, pressure-activated
strain gauge 88 connects to difference amplifier 89, which connects
to filter 90 which is in turn connected to analog-to-digital
converter 91. Note that pressure pump 87 is used to test pressure
activated strain gauge 88. Further note that both the pressure
detector and accelerometer may be simplified by using switches with
debounce circuitry in place of the combination of strain gauges,
amplifiers, filters and ADCs.
[0056] A sensor may send messages to the system, which may contain
a central panel and circuit breakers, to indicate a valid detection
indication. A sensor may also send messages to the system that
indicate a problem or a self test result. The sensor messages need
a number of elements to be effective and efficient: a sensor
identification tag, time of message or occurrence, and message type
(such as detection, self test result, interrogation response, or
anomaly report). A sensor may be programmed with its unique
identification tag. Programming may be through any number of means:
switches, flash memory, or predefined IP address.
[0057] A sensor may incorporate an array of integrated detectors
including photodetectors, pressure detectors, accelerometers, and
electronic conditioning and control circuitry onto one substrate or
circuit board or module. A single processing core, whether it is a
microcontroller, DSP, programmable logic, or fixed binary logic,
may read all the detectors, condition and fuse the data, and make a
decision regarding the validity of the detection.
[0058] There are at least two options for self test circuitry.
Built-in test (BIT), which may be manually initiated, and Built-in
Self Test (BIST), which may be automatically run, are both self
tests of the protective system. Both may run similar types of
operations and tests. In general, self test, either BIT or BIST,
should exercise individual sensors, to isolate and to identify
failed components and detectors.
[0059] Self test of a photosensor may be initiated simply by
shining a light into the photodetector 73, as shown in FIG. 8. The
self test imitates an arcing fault through a self test light 93;
the test can measure appropriate response to both a light pulse of
appropriate duration (e.g., greater than 2 or 52 milliseconds) and
to false alarm conditions where the light is too short to be
indicative of an arcing fault. This circuitry can support tests of
both the individual sensor and of the system. The sensor, as well
as the entire system, should be in a state that will not trigger
the opening of a circuit breaker during the self test.
[0060] Self test of a pressure sensor may be initiated simply by
any number of means, including closing a circuit path around the
switch in the pressure detector, using an auxiliary pressure pump,
or mechanically pulsing the diaphragm, as shown in FIG. 8. The self
test imitates an arcing fault through a pressure indication; the
test can measure appropriate response to both a pressure
representing a shockwave of appropriate duration (e.g., greater
than 1.8 milliseconds) and to false alarm conditions where the
pressure pulse is too short to be indicative of an arcing fault.
This circuitry may support tests of the individual sensor and/or
tests of the system. The sensor, as well as the entire system,
should be in a state that will not trigger the opening of a circuit
breaker during the self test.
[0061] FIG. 9 is a diagram showing one possible integrated
architecture 100 of multiple sensor modules 70 that are
individually illustrated in FIG. 7. Note that the principles of the
present application may be applied to a wide variety of
architectures 100, hence the specific integrated architecture shown
in FIG. 9 is not intended to limit the scope of this application.
Multiple sensor modules 70 each include photodetector 73,
accelerometer 74 and pressure detector 101. Processing circuitry
102 may be a microcontroller, DSP, FPGA, discrete logic or an ASIC.
Processing circuitry 102 receives the signal inputs from the
individual detectors, conditions, filters, performs threshold
comparisons fuses data and validates conditions for an arcing
fault. Processing circuitry 102 also communicates with the system
network and contains the self test circuitry (not shown). Cable
connections 103 connect processing circuitry 102 with the digital
network for communications with the protection system.
[0062] FIG. 10 is a diagram showing general schematic 110 of the
electrical circuit for the integrated architecture 100 of FIG. 9.
Pressure detectors 101 are connected to processing circuitry 102.
Individual pressure detector inputs interrupt the processing to
indicate the arrival of the acoustic pressure wave. Timers also may
be digital filters for the signal generated by pressure detectors
101. Photodetectors 73 are connected to logic gate 104. Logic gate
104 may be an "OR gate" or may possibly be a different Boolean
combination of the signals from photodetectors 73. Accelerometers
74 may be connected to signal conditioning 84, 85, 86 and to the
processing circuitry 102. Differential transceiver 105 provides
communications between microcontroller 102 and the digital
network.
[0063] Integrated architecture 100, or a variant thereof, may
provide information indicative of the direction, distance, and
location of an arcing fault. For locating an arcing fault, the
light flash triggers a timer within the processing circuitry to
time the arrival of the shock sound wave at the pressure detectors.
The time it takes between the flash and the detection of the
pressure wave is the time of flight and gives the distance to the
arcing fault. The difference in arrival times of the sound pressure
wave to two or three different pressure detectors indicates the
direction to the arcing fault from the sensor. Two pressure sensors
can give a single angle and direction in two dimensions. Three
pressure sensors can give a solid angle and direction in three
dimensions.
[0064] FIG. 11 is a diagram of one possible integrated
architecture, and more specifically shows a configuration of
pressure detectors illustrating how differences in time of flight
can indicate the angle of the wave front. Note that the principles
of the present application may be applied to a wide variety of
integrated architectures and pressure detector configurations,
hence the specific architecture and configuration of detectors
shown in FIG. 11 is not intended to limit the scope of this
application. The integrated sensor module 70 incorporates
photodiode detector 73 for detecting the bright flash from an
arcing fault. Also incorporated into integrated sensor module 70 is
pressure sensor 101 and accelerometer 74. FIG. 11 shows that the
angle .THETA..sub.1 between the propagation vector of the pressure
wave and the vector between the two pressures detectors can be
computed from: .THETA. 1 = cos - 1 [ ( .DELTA. .times. .times. t 1
* V sound ) d ] , ##EQU1## where d is the distance between pressure
detectors and .DELTA.t.sub.1 is the difference in time of arrival
of the pressure wave between two detectors.
[0065] Power for these sensors may come from either an input power
source or a back-up power source. FIG. 12 is a diagram of power
schematic 120, showing generic sensor 121, input power source 122
and backup power source 123. Input source 122 may be DC or AC
electrical power and either may be wired to each sensor. Backup
power source 123 would be used in case the power supplied on the
cable should fail, and may be either battery backup or capacitor
backup. An alternative form of backup power for the sensor network
during power failure would be a battery system or an assured
alternative power source. Note that the digital communications and
the power may easily combine onto a cable with only two wires.
[0066] The integrated sensor design disclosed in this application
uses multiple phenomenologies to define an event and increases
probability of detection while simultaneously lowering the false
alarm rate. More specifically, if one type of input is essentially
independent of another, until a specific event occurs, then their
probability of false alarm is a geometric series: P.sub.system
false alarm=.PI.P.sub.i, where the product is taken over the
independent probabilities of false alarm for all i sensor
phenomenologies.
[0067] If more independent phenomenologies are added to the system,
then the system probability of false positive alarms decreases by
multiplicative factors. Adding independent sensor phenomenologies
to the system increases the discrimination of the critical events,
which is the reason for the reduction in the rate of false positive
alarms.
[0068] In operation, when an arcing fault occurs, both light and
pressure pulses are generated. Light and pressure pulses are
detected by photodetector(s) and pressure sensor(s),
respectively.
[0069] Photodetection has several constraints to qualify as a
potential arc detection. The detection must exceed a preset
intensity threshold to trigger an indication of a potential arc.
The indication must last, i.e., exceed the intensity threshold, for
a preset amount of time (the typical range being between 2 and 52
milliseconds).
[0070] Pressure detection has several constraints to qualify as a
potential arc detection. The detection must exceed a set
differential pressure threshold to trigger an indication of a
potential arc. The indication must last, i.e., exceed the intensity
threshold, for a preset amount of time (the typical range being
between 1.8 and 20 milliseconds).
[0071] Both types of indications, light flash and pressure, must
occur nearly simultaneously before the system signals a valid
detection. Once the system receives indications from both types of
detectors in the same sensor module, then it may signal the opening
of a circuit breaker, which should extinguish the arc fault.
Considering the times already mentioned for either the photosensors
or the pressure sensors, extinction of the arc must occur somewhere
within 200 milliseconds of the first detection. This would be
considered near the upper limit. It also provides some margin in
time to discriminate the arcing fault and reduce potential false
alarms from extraneous sources. Ultimately, shorter time to
extinction is better because it reduces damage from combustion and
melting.
[0072] When an air circuit breaker opens, an arc strikes between
the contacts. The arc flash can eject from the breaker vent chute
and be detected by the sensors in the protective system. The system
that incorporates the integrated sensors of the types described
herein need to allow for circuit breaker flashes by riding through
the maximum duration allowed by code for these breaker flashovers.
This is an important timing parameter for the protective system.
The shortest time allowed for a 60 Hz power distribution
switchboard controlled by air circuit breakers is two and one half
cycles or 42.7 milliseconds. The shortest time allowed for a 50 Hz
power distribution switchboard controlled by air circuit breakers
is two and one half cycles or 50 milliseconds.
[0073] The timing for vacuum or SF6 circuit breakers is much
shorter. These types of circuit breakers are enclosed within their
own light-tight boxes. There is no path for stray light from
contact arcs to reach the outside and the sensors of the protective
system. Consequently, discrimination of a true arcing event may
happen in the 2 millisecond range or less.
[0074] This application allows for these critical timing thresholds
to be set as system parameters. Hardware registers or memory within
the sensors, in the microcontroller, DSP, FPGA, discrete logic, or
ASIC, may store these timing thresholds and use them in
discriminating an arcing fault. The parameters are: the timeout
duration for a photosensor (generally 2 to 52 milliseconds, but may
be less than 1 to greater than 60 milliseconds), the timeout
duration for a pressure sensor (generally 1.8 to 20 milliseconds,
but may be less than 1 to greater then 40 milliseconds), and the
maximum time duration allowed between a pressure sensor indication
and a photosensor indication (up to 200 milliseconds).
[0075] The integrated sensor module described herein fits into a
protection system that monitors, detects, and extinguishes arcing
faults.
[0076] Messages from the sensors are sent to the central panel and
the circuit breakers to indicate a valid detection indication.
Sensors may also send messages to the central panel that indicate a
problem or a self test result. The sensor messages need a number of
elements to be effective and efficient: a sensor identification
tag, time of message or occurrence, and message type (such as
detection, self test result, interrogation response, or anomaly
report). The interface modules for circuit breakers communicate to
the central panel with similar message types. They would have the
same format as messages from sensors.
[0077] The central panel sends and receives messages. It sends
commands to both sensors and the circuit breaker interface modules;
these commands include the following types: reset operation,
health/status interrogation, time stamp to reset time within
sensors or circuit breaker interface modules, begin normal
monitoring by sensors within the protective system, begin self
test, send results of self test, shut down operation (sent to
malfunctioning sensors and circuit breaker interface modules), send
detector's or sensor's analog reading. These commands may be either
broadcast or addressed and sent to either specific sensors or
specific circuit breaker interface modules. Its command messages
have the following format: central processing identification tag,
broadcast or address of sensor or circuit breaker interface module,
command (as listed above).
[0078] The central panel also receives messages from sensors and
circuit breaker interface modules. It records and logs these
messages for later readout or transmission to a computer external
to the protective system. The central panel may also communicate
with the outside world through an internet connection, both to run
operations and to send logs of events and operations.
[0079] Each sensor, if controlled by a local microcontroller or DSP
or FPGA or ASIC or processing element, has a generic algorithm. The
algorithm performs a number of tasks: it monitors the detectors, it
reports its identification tag when requested, it performs self
test and reports its results when requested, it reports analog
values upon request, it checks arcing indications for valid
conditions--usually a time duration and amplitude criteria--and
reports the arc indication and the validity check.
[0080] FIG. 15 is a diagram showing an example of a main algorithm
running a generic sensor. The primary operations are as follows.
From power-up and/or reset operation 131, the process moves to
operation 132 "protective monitoring operation." Operation 132 may
indicate the existence of an arc, which then causes the process to
move to operation 133 "check conditions for valid detection."
Operation 133 may declare the conditions to be valid, in which case
the process moves to operation 134 "prepare an indication message"
which is then followed by sending a message to the circuit
breakers. However, operation 133 may declare the conditions to be
invalid, then the process moves to operation 135 "prepare an
anomaly report", which is then followed by sending a message to the
central panel. At a predetermined schedule or conditions, operation
132 may request for specific stimulus for self test, in which case
operation 136 "turn on self test stimulus" is initiated. Note that
multitasking may be used to run the self test on a signal
processor, or the self test may be run on a separate processor or
processing element (i.e., microcontroller, DSP, FPGA or ASIC).
[0081] FIG. 14 shows an example of possible suboperations which
accomplish operation 133 "check conditions for valid detection"
from FIG. 13. After arc indication, operation 141 "detected arc
flash starts timers" is initiated. From operation 141 the process
moves to operation 142 "time detected arc conditions" and operation
143 "time arrival of shockwave." From operation 142 the process
moves to operation 144 "pressure timeout" or operation 145 "photo
timeout." From operation 144, if the pressure timeout is less than
(for example) 20 ms (or a preprogrammed value) then the arc
detection may be declared invalid as operation 146 and a message
declaring such an invalid detection may be transmitted. Otherwise
from operation 144, if the pressure timeout is greater than (for
example) 20 ms or a preprogrammed value, then the detection may be
declared valid as operation 147, and a message declaring such a
valid detection may be transmitted. From operation 145, if the
photo timeout is less than (for example) 50 ms (or a preprogrammed
value) then the arc detection may be declared invalid as operation
146 and a message declaring such an invalid detection may be
transmitted. Otherwise from operation 145, if the pressure timeout
is greater than (for example) 50 ms or a preprogrammed value, then
the detection may be declared valid as operation 147, and a message
declaring such a valid detection may be transmitted. From operation
143, if the time arrival of the shockwave is greater than (for
example) 8 ms or a preprogrammed value, then the process may move
to operation 135 "prepare an anomaly report" and a message
declaring the presence of an anomaly may be transmitted. Otherwise,
from operation 143, if the time arrival of the shock wave is less
than for example 8 ms or a preprogrammed value, then the process
moves to operation 148 calculate arc distance and direction and an
arc indication message may be prepared.
[0082] FIG. 15 outlines how the accelerometer input might interact
with the pressure sensor to block mechanical shock from
inappropriately triggering the pressure detector to indicate an
arcing fault. IF mechanical shock is detected by accelerometer 151,
this signal is then passed to amplifier 152 which is connected to
filter 153. From there threshold comparator 154 is employed which
sends a pulse to driver circuit 155 and on to Boolean circuit 156.
Likewise, pressure detector diaphragm 157 sends pressure signal to
pressure sensing element 158, which generates two voltage signals
which are sent to difference amplifier 159. From here, the signal
is passed to filter 160 which is connected to analog-to-digital
converter 161, which is connected to both Boolean circuit 156 and
processor element 162.
[0083] It should be apparent to those skilled in the art that the
present invention may be embodied in many other specific forms
without departing from the spirit or scope of the invention.
Therefore, the present examples and embodiments are to be
considered as illustrative and not restrictive, and the invention
is not to be limited to the details given herein, but may be
modified within the scope of the appended claims.
* * * * *